If Maria Capretz is your ancestor then this particular family is yours, they may have come to England with John her grandfather.
The name is found further north as well, it means Italians with the name Capretz have been coming to England for generations. I didn't mean to imply that your family had been traced back that far.
St Luke's Church Chelsea
Maria baptised 24 May 1801 born 15 July 1800
Mary baptised 25 August 1802 no birth date given
John William baptised 9 September 1804, born 27 July 1804 buried 3 June 1805
John baptised 20 July 1806, born 15 June 1806, buried 4 December 1812 age 6
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There is also an Elizabeth buried 3 November 1811 I've not found her baptism yet so not a definate child of John and 3rd wife Mary.
John Capretz the father of the children was buried 15 February 1824.
Hopefully he left a will or there is some sort of probate naming relatives.
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St Martin in the Fields Church
Mary Capretz married Thomas Trigg 1 October 1815, witness Mark Ringer and John Taylor.
John Taylor signs many of the entries so probably the parish clerk.
A possible sister of John.